It's unfortunate that there's still bad press circulating about a
situation that is long gone. I suppose you just have to try and
ignore those people.
A more interesting comment is this one:
"But the real problem here is that in order to achieve even that,
the complexity and amount of concepts you have to deal with in
C++11 is mind boggling."
The same is true in D. Well-written D code often does look rather
elegant, but the amount of understanding needed to write
beautiful D code is staggering.

It's unfortunate that there's still bad press circulating about
a situation that is long gone. I suppose you just have to try
and ignore those people.
A more interesting comment is this one:
"But the real problem here is that in order to achieve even
that, the complexity and amount of concepts you have to deal
with in C++11 is mind boggling."
The same is true in D. Well-written D code often does look
rather elegant, but the amount of understanding needed to write
beautiful D code is staggering.

I have to agree having to deal with lots of concepts.
On the other hand, except for the programming drones, most D
concepts are also available in most mainstream languages.
--
Paulo

A more interesting comment is this one:
"But the real problem here is that in order to achieve even that,
the complexity and amount of concepts you have to deal with in
C++11 is mind boggling."
The same is true in D. Well-written D code often does look rather
elegant, but the amount of understanding needed to write beautiful
D code is staggering.

I have to agree having to deal with lots of concepts.

I don't see it as a problem, unless one is a programmer of the drone
persuasion. Many of D's concepts are liberatingly powerful, and very
potent in combination.

On the other hand, except for the programming drones, most D
concepts are also available in most mainstream languages.

[...]
If we want to minimize the number of concepts, we should program using
Lambda calculus. ;-) We already have lambda-syntax for delegates, after
all. Now just restrict all statements to only lambda expressions, get
rid of difficult concepts like arithmetic operators, variables and
imperative programming, and we have a winner on our hands.
Seriously, though, imagining that one can program effectively without
learning new concepts is a preposterous proposition to me. I just don't
understand the unwillingness to learn.
T
--
Computers shouldn't beep through the keyhole.

A more interesting comment is this one:
"But the real problem here is that in order to achieve even
that,
the complexity and amount of concepts you have to deal with in
C++11 is mind boggling."
The same is true in D. Well-written D code often does look
rather
elegant, but the amount of understanding needed to write
beautiful
D code is staggering.

I have to agree having to deal with lots of concepts.

I don't see it as a problem, unless one is a programmer of the
drone
persuasion. Many of D's concepts are liberatingly powerful, and
very
potent in combination.

On the other hand, except for the programming drones, most D
concepts are also available in most mainstream languages.

[...]
If we want to minimize the number of concepts, we should
program using
Lambda calculus. ;-) We already have lambda-syntax for
delegates, after
all. Now just restrict all statements to only lambda
expressions, get
rid of difficult concepts like arithmetic operators, variables
and
imperative programming, and we have a winner on our hands.
Seriously, though, imagining that one can program effectively
without
learning new concepts is a preposterous proposition to me. I
just don't
understand the unwillingness to learn.
T

It is not the unwillingness to learn, rather the standard HR way
of getting replaceable programming drones in most enterprises.
This was already discussed a few times.
--
Paulo

The same is true in D. Well-written D code often does look
rather elegant, but the amount of understanding needed to write
beautiful D code is staggering.

I'll second that!
I'm finally making good progress with D after a whole lot of
effort, and there were (and still are) periods where I felt like
giving up, although not so much anymore.
The number one missing item that I would love to get my hands on
is comprehensive documentaion. What we have now leaves out far
too much detail, and may be missing entire features, and what is
available is scattered all over the place.
Reading the TDPL book is a huge help for understanding D, it's
essential reading for sure, but it's only an overview rather than
a full text on the subject. The TDPL lacks many of the fine
details that one needs to know in order to write proper D code. I
find myself experimenting a lot in order to figure out what the
various obscure details are, but without comprehensive
documentation, I cannot be certain if the observed behaviours are
actually correct or fully complete under all situations.
--rt

The same is true in D. Well-written D code often does look rather
elegant, but the amount of understanding needed to write beautiful
D code is staggering.

I'll second that!
I'm finally making good progress with D after a whole lot of effort,
and there were (and still are) periods where I felt like giving up,
although not so much anymore.
The number one missing item that I would love to get my hands on is
comprehensive documentaion. What we have now leaves out far too much
detail, and may be missing entire features, and what is available is
scattered all over the place.
Reading the TDPL book is a huge help for understanding D, it's
essential reading for sure, but it's only an overview rather than a
full text on the subject. The TDPL lacks many of the fine details
that one needs to know in order to write proper D code. I find
myself experimenting a lot in order to figure out what the various
obscure details are, but without comprehensive documentation, I
cannot be certain if the observed behaviours are actually correct or
fully complete under all situations.

Ali's D book might be helpful: http://ddili.org/ders/d.en/index.html
But yeah, the current documentation needs work. Unfortunately, wishing
for it to happen won't make it happen, so if you contribute (use the
"improve this page" link) that would be great, and suggestions are also
helpful. I recently revised the docs for std.range to explain briefly
what ranges are and why we even need them, but this is only one piece of
the entire standard library. Many other modules need improved docs. And
there is still the need for a general overview to put everything in
perspective.
T
--
It is impossible to make anything foolproof because fools are so ingenious. --
Sammy

But yeah, the current documentation needs work. Unfortunately,
wishing
for it to happen won't make it happen, so if you contribute
(use the
"improve this page" link) that would be great

I never noticed that link before. When I click on it, I go to
github showing me a webpage with "404" on it. The text over link
says I need a github account and to submit pull requests. I'm not
sure how I'm supposed to make changes with that.
I know about the regular Wiki and have made a contribution there,
that's very simple to do.
--rt

But yeah, the current documentation needs work. Unfortunately,
wishing
for it to happen won't make it happen, so if you contribute
(use the
"improve this page" link) that would be great

I never noticed that link before. When I click on it, I go to
github showing me a webpage with "404" on it. The text over
link says I need a github account and to submit pull requests.
I'm not sure how I'm supposed to make changes with that.
I know about the regular Wiki and have made a contribution
there, that's very simple to do.
--rt

All the documentation is written in DDoc. The website is hosted
on github. Github provides an online text editor usable against
your repository. Your repository is created as a fork of the
original. Github uses pull requests to move changes upstream.
It isn't as simple as a wiki but it isn't too bad. Hope that is
enough information to get started.

The number one missing item that I would love to get my hands
on is comprehensive documentaion. What we have now leaves out
far too much detail, and may be missing entire features, and
what is available is scattered all over the place.

Workaround: I find it useful to check the code of a 'std' module
that interests me. A lot of unittests and comments are quite
usefull. For ex. about the RAII/ref-counted stuff I checked the
stdio.d File.

The same is true in D. Well-written D code often does look
rather elegant, but the amount of understanding needed to write
beautiful D code is staggering.

It's almost impossible to keep languages simple. Some complexity
comes from the desire to do more and more. As example see this
recent request from Manu, it's simple, but it also increases the
complexity of D:
http://d.puremagic.com/issues/show_bug.cgi?id=8108
Bye,
bearophile

Some complexity comes from the
desire to do more and more. As example see this recent request from Manu,

What about all your feature requests? I think you've made more than anyone, by
a
factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable way.
He
needs it for real code in a real application.

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented. Although I think something like
AST macros could possible solve issue 8108 and a whole bunch of other
features, a few already present in the language.
--
/Jacob Carlborg

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented.

He just knows how to convince Walter.
(Hint: use real-world use cases. Arguments from theoretical computer
science carry almost no weight with Walter).

Although I think something like
AST macros could possible solve issue 8108 and a whole bunch of other
features, a few already present in the language.

Yes, and they could cure cancer. "AST macros" can do anything, because
they are completely undefined. Without even a vague proposal, it seems
like a rather meaningless term.

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented.

He just knows how to convince Walter.
(Hint: use real-world use cases. Arguments from theoretical computer
science carry almost no weight with Walter).

I think there are lots of issues in the bug tracker which describe real
use cases. The point is that these are more like bugs whereas Manu's
proposals are more like feature requests.
Jens

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented.

He just knows how to convince Walter.
(Hint: use real-world use cases. Arguments from theoretical computer
science carry almost no weight with Walter).

I think there are lots of issues in the bug tracker which describe real
use cases. The point is that these are more like bugs whereas Manu's
proposals are more like feature requests.
Jens

The SIMD stuff has no workarounds. I don't know of many other feature
requests in that category.

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented.

He just knows how to convince Walter.
(Hint: use real-world use cases. Arguments from theoretical computer
science carry almost no weight with Walter).

I think there are lots of issues in the bug tracker which describe real
use cases. The point is that these are more like bugs whereas Manu's
proposals are more like feature requests.
Jens

The SIMD stuff has no workarounds. I don't know of many other
feature requests in that category.

Then I have a serious misunderstanding.
I thought D introduced array operations to allow the compiler to
generate efficient vector operations (in the long run), i.e. generate
SIMD code. Why is this not working out?
Jens

Then I have a serious misunderstanding.
I thought D introduced array operations to allow the compiler to
generate efficient vector operations (in the long run), i.e.
generate
SIMD code. Why is this not working out?

It works fine for large vectors. For small vectors, it is
horrendously slow.
The syntax a[] += b[] essentially calls a function which is
designed to work for large vectors. It has to determine
alignment, load everything from memory, do the operations, then
store it back.
The SIMD extensions allow you to define variables that are
guaranteed to be aligned and will probably be in the right
registers to start with. Using them, the vectors ops don't need
to determine alignment, and often don't need to do lots of
loads/stores.
Both have their purposes.

Then I have a serious misunderstanding.
I thought D introduced array operations to allow the compiler to
generate efficient vector operations (in the long run), i.e.
generate
SIMD code. Why is this not working out?

It works fine for large vectors. For small vectors, it is
horrendously slow.
The syntax a[] += b[] essentially calls a function which is designed
to work for large vectors. It has to determine alignment, load
everything from memory, do the operations, then store it back.
The SIMD extensions allow you to define variables that are
guaranteed to be aligned and will probably be in the right registers
to start with. Using them, the vectors ops don't need to determine
alignment, and often don't need to do lots of loads/stores.
Both have their purposes.

I see. But can't the alignment problem be solved by using align. Then
have the compiler emits a call that checks for alignment if none was
specified else use a faster version.
Jens

Then I have a serious misunderstanding.
I thought D introduced array operations to allow the compiler to
generate efficient vector operations (in the long run), i.e.
generate
SIMD code. Why is this not working out?

It works fine for large vectors. For small vectors, it is
horrendously slow.
The syntax a[] += b[] essentially calls a function which is designed
to work for large vectors. It has to determine alignment, load
everything from memory, do the operations, then store it back.
The SIMD extensions allow you to define variables that are
guaranteed to be aligned and will probably be in the right registers
to start with. Using them, the vectors ops don't need to determine
alignment, and often don't need to do lots of loads/stores.
Both have their purposes.

I see. But can't the alignment problem be solved by using align. Then
have the compiler emits a call that checks for alignment if none was
specified else use a faster version.

No. For SIMD, you cannot afford to have even a single machine
instruction inserted, or the benefit is entirely lost.

Then I have a serious misunderstanding.
I thought D introduced array operations to allow the compiler to
generate efficient vector operations (in the long run), i.e.
generate
SIMD code. Why is this not working out?

It works fine for large vectors. For small vectors, it is
horrendously slow.
The syntax a[] += b[] essentially calls a function which is designed
to work for large vectors. It has to determine alignment, load
everything from memory, do the operations, then store it back.
The SIMD extensions allow you to define variables that are
guaranteed to be aligned and will probably be in the right registers
to start with. Using them, the vectors ops don't need to determine
alignment, and often don't need to do lots of loads/stores.
Both have their purposes.

I see. But can't the alignment problem be solved by using align. Then
have the compiler emits a call that checks for alignment if none was
specified else use a faster version.

No. For SIMD, you cannot afford to have even a single machine
instruction inserted, or the benefit is entirely lost.

But the compiler knows about the alignment, doesn't it?
align(16) float[4] a;
vs
float[4] a;
In the former case the compiler can generate better code and it should.
The above syntax is not supported. But my point is all the compiler
cares about is the alignment which can be specified in the code somehow.
Sorry for being stubborn.
Jens

But the compiler knows about the alignment, doesn't it?
align(16) float[4] a;
vs
float[4] a;
In the former case the compiler can generate better code and it
should.
The above syntax is not supported. But my point is all the
compiler
cares about is the alignment which can be specified in the code
somehow.
Sorry for being stubborn.
Jens

Note: My knowledge of SIMD/SSE is fairly limited, and may be
somewhat out of date. In other words, some of this may be flat
out wrong.
First, just because you have something that can have SIMD
operations performed on it, doesn't mean you necessarily want to.
SSE instructions for example have to store things in the XMM
registers, and accessing the actual values of individual elements
in the vector is expensive. When using SSE, you want to avoid
accessing individual elements as much as possible. Not following
this tends to hurt performance quite badly. Yet when you just
have a float[4], you may or may not be frequently or infrequently
accessing individual elements. The compiler can't know whether
you use it as a single SIMD vector more often, or use it to
simply store 4 elements more often. You could be aligning it for
any reason, so it's not too fair a way of determining it.
Secondly, you can't really know which SIMD instructions are
supported by your target CPU. It's safe to say SSE2 is supported
for pretty much all x86 CPUs at this point, but something like
SSE4.2 instructions may not be. Just because the compiler knows
that the CPU compiling it supports it doesn't mean that the CPU
running the program will have those instructions.
Lastly, we'd still need SIMD intrinsics. It may be simple to tell
that a float[4] + float[4] operation could use addps, but it
would be more difficult to determine when to use something like
dotps (dot product across two SIMD vectors), and various other
instructions. Not to mention, non-x86 architectures.

What about all your feature requests? I think you've made
more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other
reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically
nowhere and
fairly quickly manage to convince Walter to implement at least
two
feature requests, this one and the SIMD support. I'm not
saying that
they shouldn't have been implemented.

He just knows how to convince Walter.
(Hint: use real-world use cases. Arguments from theoretical
computer science carry almost no weight with Walter).

Although I think something like
AST macros could possible solve issue 8108 and a whole bunch
of other
features, a few already present in the language.

Yes, and they could cure cancer. "AST macros" can do anything,
because they are completely undefined. Without even a vague
proposal, it seems like a rather meaningless term.

How do you think people came up with those bug reports? By some
magic? :) You think they did not actually *pull their hair off*
trying to figure out why their REAL LIFE program does not work,
and when we could not find the reason we naturally started
thinking "oh, it might be yet another missing thing in D" or "oh,
yet another DMD/phobos/druntime bug!"...
Or, another scenario (a very typical one) - after
DMD/phobos/druntime is updated, my production application no
longer compiles...

How do you think people came up with those bug reports? By some magic?
:) You think they did not actually *pull their hair off* trying to
figure out why their REAL LIFE program does not work, and when we could
not find the reason we naturally started thinking "oh, it might be yet
another missing thing in D" or "oh, yet another DMD/phobos/druntime
bug!"...
Or, another scenario (a very typical one) - after DMD/phobos/druntime is
updated, my production application no longer compiles...

Good point. When you do put the whole real life program in the bug
report "it's too big, you need to create a small test case". When you do
create a small test case for the feature/bug it's suddenly not "real
life" code.
--
/Jacob Carlborg

Yes, and they could cure cancer. "AST macros" can do anything, because
they are completely undefined. Without even a vague proposal, it seems
like a rather meaningless term.

I know, I know. It's be brought up before and without any more detailed
specification/definition is hard to do anything about it. I've done some
research in the subject in the hope I can write down something useful
that could be a proposal for D, but I don't have anything yet.
--
/Jacob Carlborg

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented. Although I think something
like AST macros could possible solve issue 8108 and a whole bunch of
other features, a few already present in the language.

I had the same thought when reading this. Very disappointing. An issue
with zero votes is fixed instead of more important ones. Why do I vote
anyway?
Regarding SIMD I have the feeling that because it is built into the
compiler static vectors have actually failed what they promised. I
thought D proposed a portable way of vector operations such that you
write
float[4] = a[] + b[]
and the compiler generates SIMD code for you.
Jens

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented. Although I think something
like AST macros could possible solve issue 8108 and a whole bunch of
other features, a few already present in the language.

I had the same thought when reading this. Very disappointing. An issue
with zero votes is fixed instead of more important ones. Why do I vote
anyway?
Regarding SIMD I have the feeling that because it is built into the
compiler static vectors have actually failed what they promised. I
thought D proposed a portable way of vector operations such that you
write
float[4] = a[] + b[]
and the compiler generates SIMD code for you.

Not for short vectors. They are more like the builtin operations in
Fortran, ie designed for large vectors. More for scientific kinds of
applications than games. (The two applications look superficially
similar, but in practice they have little in common).

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented. Although I think something
like AST macros could possible solve issue 8108 and a whole bunch of
other features, a few already present in the language.

I had the same thought when reading this. Very disappointing. An issue
with zero votes is fixed instead of more important ones. Why do I vote
anyway?
Regarding SIMD I have the feeling that because it is built into the
compiler static vectors have actually failed what they promised. I
thought D proposed a portable way of vector operations such that you
write
float[4] = a[] + b[]
and the compiler generates SIMD code for you.

Not for short vectors. They are more like the builtin operations in
Fortran, ie designed for large vectors. More for scientific kinds of
applications than games. (The two applications look superficially
similar, but in practice they have little in common).

Okay. For me they look the same. Can you elaborate, please? Assume I
want to add two float vectors which is common in both games and
scientific computing. The only difference is in games their length is
usually 3 or 4 whereas in scientific computing they are of arbitrary
length. Why do I need instrinsics to support the game setting?
Jens

What about all your feature requests? I think you've made
more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no
other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically
nowhere and
fairly quickly manage to convince Walter to implement at
least two
feature requests, this one and the SIMD support. I'm not
saying that
they shouldn't have been implemented. Although I think
something
like AST macros could possible solve issue 8108 and a whole
bunch of
other features, a few already present in the language.

I had the same thought when reading this. Very disappointing.
An issue
with zero votes is fixed instead of more important ones. Why
do I vote
anyway?
Regarding SIMD I have the feeling that because it is built
into the
compiler static vectors have actually failed what they
promised. I
thought D proposed a portable way of vector operations such
that you
write
float[4] = a[] + b[]
and the compiler generates SIMD code for you.

Not for short vectors. They are more like the builtin
operations in
Fortran, ie designed for large vectors. More for scientific
kinds of
applications than games. (The two applications look
superficially
similar, but in practice they have little in common).

Okay. For me they look the same. Can you elaborate, please?
Assume I
want to add two float vectors which is common in both games and
scientific computing. The only difference is in games their
length is
usually 3 or 4 whereas in scientific computing they are of
arbitrary
length. Why do I need instrinsics to support the game setting?
Jens

The auto vectorization code in Visual Studio 2012 seems to work
pretty well.

Okay. For me they look the same. Can you elaborate, please? Assume I
want to add two float vectors which is common in both games and
scientific computing. The only difference is in games their length is
usually 3 or 4 whereas in scientific computing they are of arbitrary
length. Why do I need instrinsics to support the game setting?

Another excellent question.
Most languages have taken the "auto-vectorization" approach of reverse
engineering loops to turn them into high level constructs, and then compiling
the code into special SIMD instructions.
How to do this is explained in detail in the (rare) book "The Software
Vectorization Handbook" by Bik, which I fortunately was able to obtain a copy
of.
This struck me as a terrible approach, however. It just seemed stupid to try to
teach the compiler to reverse engineer low level code into high level code. A
better design would be to start with high level code. Hence, the appearance of
D
vector operations.
The trouble with D vector operations, however, is that they are too general
purpose. The SIMD instructions are very quirky, and it's easy to unwittingly
and
silently cause the compiler to generate absolutely terribly slow code. The
reasons for that are the alignment requirements, coupled with the SIMD
instructions not being orthogonal - some operations work for some types and not
for others, in a way that is unintuitive unless you're carefully reading the
SIMD specs.
Just saying align(16) isn't good enough, as the vector ops work on slices and
those slices aren't always aligned. So each one has to check alignment at
runtime, which is murder on performance.
If a particular vector op for a particular type has no SIMD support, then the
compiler has to generate workaround code. This can also have terrible
performance consequences.
So the user writes vector code, benchmarks it, finds zero improvement, and the
reasons why will be elusive to anyone but an expert SIMD programmer.
(Auto-vectorizing technology has similar issues, pretty much meaning you won't
get fast code out of it unless you've got a habit of examining the assembler
output and tweaking as necessary.)
Enter Manu, who has a lot of experience making SIMD work for games. His
proposal
was:
1. Have native SIMD types. This will guarantee alignment, and will guarantee a
compile time error for SIMD types that are not supported by the CPU.
2. Have the compiler issue an error for SIMD operations that are not supported
by the CPU, rather than silently generating inefficient workaround code.
3. There are all kinds of weird but highly useful SIMD instructions that don't
have a straightforward representation in high level code, such as saturated
arithmetic. Manu's answer was to expose these instructions via intrinsics, so
the user can string them together, be sure that they will generate real SIMD
instructions, while the compiler can deal with register allocation.
This approach works, is inlineable, generates code as good as hand-built
assembler, and is useable by regular programmers.
I won't say there aren't better approaches, but this one we know works.

Okay. For me they look the same. Can you elaborate, please? Assume I
want to add two float vectors which is common in both games and
scientific computing. The only difference is in games their length is
usually 3 or 4 whereas in scientific computing they are of arbitrary
length. Why do I need instrinsics to support the game setting?

Another excellent question.
Most languages have taken the "auto-vectorization" approach of reverse
engineering loops to turn them into high level constructs, and then
compiling the code into special SIMD instructions.
How to do this is explained in detail in the (rare) book "The Software
Vectorization Handbook" by Bik, which I fortunately was able to obtain a
copy of.
This struck me as a terrible approach, however. It just seemed stupid to
try to teach the compiler to reverse engineer low level code into high
level code. A better design would be to start with high level code. Hence,
the appearance of D vector operations.
The trouble with D vector operations, however, is that they are too
general purpose. The SIMD instructions are very quirky, and it's easy to
unwittingly and silently cause the compiler to generate absolutely terribly
slow code. The reasons for that are the alignment requirements, coupled
with the SIMD instructions not being orthogonal - some operations work for
some types and not for others, in a way that is unintuitive unless you're
carefully reading the SIMD specs.
Just saying align(16) isn't good enough, as the vector ops work on slices
and those slices aren't always aligned. So each one has to check alignment
at runtime, which is murder on performance.
If a particular vector op for a particular type has no SIMD support, then
the compiler has to generate workaround code. This can also have terrible
performance consequences.
So the user writes vector code, benchmarks it, finds zero improvement, and
the reasons why will be elusive to anyone but an expert SIMD programmer.
(Auto-vectorizing technology has similar issues, pretty much meaning you
won't get fast code out of it unless you've got a habit of examining the
assembler output and tweaking as necessary.)
Enter Manu, who has a lot of experience making SIMD work for games. His
proposal was:
1. Have native SIMD types. This will guarantee alignment, and will
guarantee a compile time error for SIMD types that are not supported by the
CPU.
2. Have the compiler issue an error for SIMD operations that are not
supported by the CPU, rather than silently generating inefficient
workaround code.
3. There are all kinds of weird but highly useful SIMD instructions that
don't have a straightforward representation in high level code, such as
saturated arithmetic. Manu's answer was to expose these instructions via
intrinsics, so the user can string them together, be sure that they will
generate real SIMD instructions, while the compiler can deal with register
allocation.

Well, I wouldn't claim any credit for the approach ;) .. I think this is
the standard for maximum performance, and also very well understood.
But the thing that excites me most is the potential quality of libraries
that can be built on top. D has so much potential to extend on this SIMD
foundation with it's templates being able to intelligently handle far more
context specific situations.
What we do already in other languages will be far more convenient, more
portable, and possibly even produce better code in D. And the biggest
bonus, it will be readable! :)
I think it's a low risk investment, and it doesn't prohibit higher level
support in the future.
This approach works, is inlineable, generates code as good as hand-built

assembler, and is useable by regular programmers.
I won't say there aren't better approaches, but this one we know works.

Aye, and it's relatively un-intrusive too. Some new types and a few
intrinsics, build useful libraries on top. It shouldn't have complex side
effects, and if offers something that was sorely missing from the language
today.

Okay. For me they look the same. Can you elaborate, please? Assume I
want to add two float vectors which is common in both games and
scientific computing. The only difference is in games their length is
usually 3 or 4 whereas in scientific computing they are of arbitrary
length. Why do I need instrinsics to support the game setting?

Another excellent question.
Most languages have taken the "auto-vectorization" approach of
reverse engineering loops to turn them into high level constructs,
and then compiling the code into special SIMD instructions.
How to do this is explained in detail in the (rare) book "The
Software Vectorization Handbook" by Bik, which I fortunately was
able to obtain a copy of.
This struck me as a terrible approach, however. It just seemed
stupid to try to teach the compiler to reverse engineer low level
code into high level code. A better design would be to start with
high level code. Hence, the appearance of D vector operations.
The trouble with D vector operations, however, is that they are too
general purpose. The SIMD instructions are very quirky, and it's
easy to unwittingly and silently cause the compiler to generate
absolutely terribly slow code. The reasons for that are the
alignment requirements, coupled with the SIMD instructions not being
orthogonal - some operations work for some types and not for others,
in a way that is unintuitive unless you're carefully reading the
SIMD specs.
Just saying align(16) isn't good enough, as the vector ops work on
slices and those slices aren't always aligned. So each one has to
check alignment at runtime, which is murder on performance.
If a particular vector op for a particular type has no SIMD support,
then the compiler has to generate workaround code. This can also
have terrible performance consequences.
So the user writes vector code, benchmarks it, finds zero
improvement, and the reasons why will be elusive to anyone but an
expert SIMD programmer.
(Auto-vectorizing technology has similar issues, pretty much meaning
you won't get fast code out of it unless you've got a habit of
examining the assembler output and tweaking as necessary.)
Enter Manu, who has a lot of experience making SIMD work for games.
His proposal was:
1. Have native SIMD types. This will guarantee alignment, and will
guarantee a compile time error for SIMD types that are not supported
by the CPU.
2. Have the compiler issue an error for SIMD operations that are not
supported by the CPU, rather than silently generating inefficient
workaround code.
3. There are all kinds of weird but highly useful SIMD instructions
that don't have a straightforward representation in high level code,
such as saturated arithmetic. Manu's answer was to expose these
instructions via intrinsics, so the user can string them together,
be sure that they will generate real SIMD instructions, while the
compiler can deal with register allocation.
This approach works, is inlineable, generates code as good as
hand-built assembler, and is useable by regular programmers.
I won't say there aren't better approaches, but this one we know works.

I see. Thanks for clarifying.
If I want fast vector operations I have to use core.simd. The built-in
vector operations won't fit the bill. I was of the opinion that a vector
operation in D should (at some point) generate vectorized code.
Jens

I see. Thanks for clarifying.
If I want fast vector operations I have to use core.simd. The built-in
vector operations won't fit the bill.

I think a better quote would be "If i want *HARDWARE* vector
operations..."; this is not automatically faster by nature, it requires
strict self-control in terms of application, and very careful attention if
you want your code to be portable.
At the moment, yes.

However, Manu is working on developing a higher order layer.

I have a fork; some people are using it already. It still needs a lot of
work though; some compilers missing parts, platforms not supported.
That said, it's not an effort to address D's natural vector syntax, the key
goal is to provide a hardware SIMD API that is as orthogonal as possible
and portable (with confidence it will run reasonably well).
I wonder if druntime could be enhanced to use the SIMD stuff though in the
functions that perform the natural vector operations, might offer some nice
little boosts.

I see. Thanks for clarifying.
If I want fast vector operations I have to use core.simd. The built-in
vector operations won't fit the bill.

I think a better quote would be "If i want *HARDWARE* vector
operations..."; this is not automatically faster by nature, it requires
strict self-control in terms of application, and very careful attention if
you want your code to be portable.
At the moment, yes.

However, Manu is working on developing a higher order layer.

I have a fork; some people are using it already. It still needs a lot of
work though; some compilers missing parts, platforms not supported.
That said, it's not an effort to address D's natural vector syntax, the key
goal is to provide a hardware SIMD API that is as orthogonal as possible
and portable (with confidence it will run reasonably well).
I wonder if druntime could be enhanced to use the SIMD stuff though in the
functions that perform the natural vector operations, might offer some nice
little boosts.

Cool.
It'll be nice though if D's vector operations could be expressed on top
of it. I mean a[] + b[] is so much easier to read.
Jens

I have a fork; some people are using it already. It still needs a lot of
work though; some compilers missing parts, platforms not supported.
That said, it's not an effort to address D's natural vector syntax, the
key
goal is to provide a hardware SIMD API that is as orthogonal as possible
and portable (with confidence it will run reasonably well).
I wonder if druntime could be enhanced to use the SIMD stuff though in
the
functions that perform the natural vector operations, might offer some
nice
little boosts.

Cool.
It'll be nice though if D's vector operations could be expressed on top
of it. I mean a[] + b[] is so much easier to read.

Perhaps I'm the confused one here, but as I understand it, that's the
whole point of the latter part of the paragraph - array operations are
implemented in druntime, and that implementation might benefit from using
SIMD instructions.
--
Simen

I have a fork; some people are using it already. It still needs a lot of
work though; some compilers missing parts, platforms not supported.
That said, it's not an effort to address D's natural vector
syntax, the key
goal is to provide a hardware SIMD API that is as orthogonal as possible
and portable (with confidence it will run reasonably well).
I wonder if druntime could be enhanced to use the SIMD stuff
though in the
functions that perform the natural vector operations, might
offer some nice
little boosts.

Cool.
It'll be nice though if D's vector operations could be expressed on top
of it. I mean a[] + b[] is so much easier to read.

Perhaps I'm the confused one here, but as I understand it, that's the
whole point of the latter part of the paragraph - array operations are
implemented in druntime, and that implementation might benefit from using
SIMD instructions.

I had the same thought when reading this. Very disappointing. An issue
with zero votes is fixed instead of more important ones.

It's a very fair question.
Manu works for Remedy Games, a developer of hit PC games, such as Max Payne and
Alan Wake. He champions a team that is investigating committing to D for a
major
new game. This would be a huge design win for D, and an enormous boost for D. I
view the most effective use of my time at the moment is to ensure that they can
bet on D and win. Remedy's use of D for a high profile product will prove that
D
is ready and able for the big time, and that others can develop using D with
confidence.
Nearly all of what he needs the D community needs anyway, such as the big push
for Win64 support and the SIMD support (more on that in another post).

Manu works for Remedy Games, a developer of hit PC games, such as Max Payne
and
Alan Wake. He champions a team that is investigating committing to D for a
major
new game.

Wow that's really cool!
Manu if you know of any trivial-type bugs you'd like to get fixed (for
example error messages) let me know so I can prioritize them. There's
a ton of open issues and I usually select the ones for fixing by
random. I've managed to fix a few so far. :)

Manu if you know of any trivial-type bugs you'd like to get fixed (for
example error messages) let me know so I can prioritize them. There's
a ton of open issues and I usually select the ones for fixing by
random. I've managed to fix a few so far. :)

Thanks, any help would be appreciated. I'll ask Manu for a list of his priority
issues, and even minor ones.
What will also help is trying out the beta Win64 target. I've been posting
nightly new betas for it.

On 11/2/2012 2:01 AM, Jens Mueller wrote:
> I had the same thought when reading this. Very disappointing. An issue
> with zero votes is fixed instead of more important ones.
It's a very fair question.
Manu works for Remedy Games, a developer of hit PC games, such as Max
Payne and Alan Wake. He champions a team that is investigating
committing to D for a major new game. This would be a huge design win
for D, and an enormous boost for D. I view the most effective use of my
time at the moment is to ensure that they can bet on D and win. Remedy's
use of D for a high profile product will prove that D is ready and able
for the big time, and that others can develop using D with confidence.
Nearly all of what he needs the D community needs anyway, such as the
big push for Win64 support and the SIMD support (more on that in another
post).

I should add that I'm also totally behind this. When Walter jumped into
implementing SIMD support on a hunch, I completely disagreed, but that
was a great decision.
Andrei

I had the same thought when reading this. Very disappointing. An issue
with zero votes is fixed instead of more important ones.

It's a very fair question.
Manu works for Remedy Games, a developer of hit PC games, such as Max
Payne and Alan Wake. He champions a team that is investigating
committing to D for a major new game. This would be a huge design win
for D, and an enormous boost for D. I view the most effective use of my
time at the moment is to ensure that they can bet on D and win. Remedy's
use of D for a high profile product will prove that D is ready and able
for the big time, and that others can develop using D with confidence.
Nearly all of what he needs the D community needs anyway, such as the
big push for Win64 support and the SIMD support (more on that in another
post).

I should add that I'm also totally behind this. When Walter jumped into
implementing SIMD support on a hunch, I completely disagreed, but that
was a great decision.
Andrei

I had the same thought when reading this. Very disappointing. An issu=

e

with zero votes is fixed instead of more important ones.

It's a very fair question.
Manu works for Remedy Games, a developer of hit PC games, such as Max
Payne and Alan Wake. He champions a team that is investigating
committing to D for a major new game. This would be a huge design win
for D, and an enormous boost for D. I view the most effective use of my
time at the moment is to ensure that they can bet on D and win. Remedy'=

s

use of D for a high profile product will prove that D is ready and able
for the big time, and that others can develop using D with confidence.
Nearly all of what he needs the D community needs anyway, such as the
big push for Win64 support and the SIMD support (more on that in anothe=

r

post).

I should add that I'm also totally behind this. When Walter jumped into
implementing SIMD support on a hunch, I completely disagreed, but that
was a great decision.
Andrei

I still don't understand the benefice over align(16) float[4] .

It's a mechanism to insist on register placement and usage semantics. On
the vast majority of architectures, floats and simd are absolutely
incompatible. It's awfully dangerous to describe them both with a single
type when they are mutually exclusive...

I should add that I'm also totally behind this. When Walter jumped into
implementing SIMD support on a hunch, I completely disagreed, but that
was a great decision.

I can absolutely understand why he did it but it would be really nice if
you (Walter, Andrei and probably others as well) could be more
transparent about things like these. I think this would really help the
community.
--
/Jacob Carlborg

I should add that I'm also totally behind this. When Walter jumped into
implementing SIMD support on a hunch, I completely disagreed, but that
was a great decision.

I can absolutely understand why he did it but it would be really nice if
you (Walter, Andrei and probably others as well) could be more
transparent about things like these. I think this would really help the
community.

I should add that I'm also totally behind this. When Walter
jumped into
implementing SIMD support on a hunch, I completely disagreed,
but that
was a great decision.

I can absolutely understand why he did it but it would be
really nice if you (Walter, Andrei and probably others as well)
could be more transparent about things like these. I think this
would really help the community.

So true. Strong mid-term vision of rationales of main language
developers really helps to reason about it.

I should add that I'm also totally behind this. When Walter jumped into
implementing SIMD support on a hunch, I completely disagreed, but that
was a great decision.

I can absolutely understand why he did it but it would be really nice
if you (Walter, Andrei and probably others as well) could be more
transparent about things like these. I think this would really help
the community.

So true. Strong mid-term vision of rationales of main language
developers really helps to reason about it.

I can absolutely understand why he did it but it would be really nice if you
(Walter, Andrei and probably others as well) could be more transparent about
things like these. I think this would really help the community.

I apologize for being circumspect about this, but I have to respect peoples'
privacy and I cleared what I posted about Remedy with them before posting it.

I can absolutely understand why he did it but it would be really nice if
you
(Walter, Andrei and probably others as well) could be more transparent
about
things like these. I think this would really help the community.

I apologize for being circumspect about this, but I have to respect
peoples' privacy and I cleared what I posted about Remedy with them before
posting it.

That said, I think we'd perhaps appreciate that it doesn't appear all over
the internets just yet. It would be much more interesting, and probably
have a lot more impact if we made such an announcement alongside something
to show.

I apologize for being circumspect about this, but I have to respect
peoples' privacy and I cleared what I posted about Remedy with them
before posting it.

This has nothing to do with what Manu does for a living (sure,
mentioning Remedy gives it more weight, at least for me). It's more in
the line of creating a post/starting a new thread saying something like:
"After a throughout discussion with Manu (or 'a fellow D programmer' if
he/she prefers to be anonymous) we have decided it would be in best
interest of D if we implement this particular feature. From now on this
is where I will focus most most of my time".
Something like this would be far better then suddenly seeing commits
regarding SIMD (or whatever feature it might be) for out of the blue.
--
/Jacob Carlborg

"After a throughout discussion with Manu (or 'a fellow D
programmer' if he/she prefers to be anonymous) we have decided
it would be in best interest of D if we implement this
particular feature. From now on this is where I will focus most
most of my time".
Something like this would be far better then suddenly seeing
commits regarding SIMD (or whatever feature it might be) for
out of the blue.

I can absolutely understand why he did it but it would be really nice if you
(Walter, Andrei and probably others as well) could be more transparent about
things like these. I think this would really help the community.

I apologize for being circumspect about this, but I have to respect
peoples' privacy and I cleared what I posted about Remedy with them
before posting it.

There is no need to reveal anything private just because you have a road
map.
Jens

On 2012-11-02 18:46, Andrei Alexandrescu wrote:
I should add that I'm also totally behind this. When Walter jumped into

implementing SIMD support on a hunch, I completely disagreed, but that
was a great decision.

I can absolutely understand why he did it but it would be really nice if
you (Walter, Andrei and probably others as well) could be more transparent
about things like these. I think this would really help the community.

This is probably my fault, and a matter of corporate transparency. We
didn't want to make a noise about it until we reached a particular level of
confidence.
We're fairly invested now, and quietly hopeful it will go ahead from here.

This is probably my fault, and a matter of corporate transparency. We
didn't want to make a noise about it until we reached a particular level
of confidence.
We're fairly invested now, and quietly hopeful it will go ahead from here.

This has nothing to do with corporate transparency. It has to do with
transparency to the community, see my reply to Walter:
http://forum.dlang.org/thread/jauixhakwvpgsghapzvz forum.dlang.org?page=6#post-k718iu:242iu6:241:40digitalmars.com
--
/Jacob Carlborg

I had the same thought when reading this. Very disappointing. An issue
with zero votes is fixed instead of more important ones.

It's a very fair question.
Manu works for Remedy Games, a developer of hit PC games, such as Max
Payne and Alan Wake. He champions a team that is investigating
committing to D for a major new game. This would be a huge design win
for D, and an enormous boost for D. I view the most effective use of my
time at the moment is to ensure that they can bet on D and win. Remedy's
use of D for a high profile product will prove that D is ready and able
for the big time, and that others can develop using D with confidence.
Nearly all of what he needs the D community needs anyway, such as the
big push for Win64 support and the SIMD support (more on that in another
post).

I should add that I'm also totally behind this. When Walter jumped
into implementing SIMD support on a hunch, I completely disagreed,
but that was a great decision.

From the inside you can tell it is a great decision. From the outside it

It's a very fair question.
Manu works for Remedy Games, a developer of hit PC games, such as Max
Payne and Alan Wake. He champions a team that is investigating
committing to D for a major new game. This would be a huge design win
for D, and an enormous boost for D. I view the most effective use of my
time at the moment is to ensure that they can bet on D and win. Remedy's
use of D for a high profile product will prove that D is ready and able
for the big time, and that others can develop using D with confidence.
Nearly all of what he needs the D community needs anyway, such as the
big push for Win64 support and the SIMD support (more on that in another
post).

I can absolutely see the point in this. Thanks for taking the time and
explaining this.
--
/Jacob Carlborg

and
Alan Wake. He champions a team that is investigating committing to D for

a

major
new game.

Wow that's really cool!
Manu if you know of any trivial-type bugs you'd like to get fixed (for
example error messages) let me know so I can prioritize them. There's
a ton of open issues and I usually select the ones for fixing by
random. I've managed to fix a few so far. :)

I had the same thought when reading this. Very disappointing. An issue
with zero votes is fixed instead of more important ones.

It's a very fair question.
Manu works for Remedy Games, a developer of hit PC games, such as
Max Payne and Alan Wake. He champions a team that is investigating
committing to D for a major new game. This would be a huge design
win for D, and an enormous boost for D. I view the most effective
use of my time at the moment is to ensure that they can bet on D and
win. Remedy's use of D for a high profile product will prove that D
is ready and able for the big time, and that others can develop
using D with confidence.
Nearly all of what he needs the D community needs anyway, such as
the big push for Win64 support and the SIMD support (more on that in
another post).

Now I can understand why you made these decisions. It makes sense to me.
But I'd like to know which direction the ship is sailing.
The current rationale is to proof that D is ready for prime time. Though
I fear that some issues in the bug tracker may give a bad impression.
But in general the decision process should be as open and transparent as
possible. In Jacob's words: We need a road map.
Jens

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented.

SIMD support is necessary and the fix for 8108 is very simple. If the
way default arguments work shall be improved though, it would add
additional ways that the compiler can screw up conditional compilation.

Although I think something like
AST macros could possible solve issue 8108 and a whole bunch of other
features, a few already present in the language.

A sufficiently well/badly designed macro feature can potentially replace
most other language features.

Uh oh, I just caught wind of this thread! ;)
If there's a single argument I'd like to make in defense of the changes
that have gone through as a result of my motivating, it's that they're
either big tickets and mutually beneficial for the whole community anyway
(DMD-win64), or relatively trivial (function prototypes + definitions)
details that enable us to realistically consider proceeding with D
commercially.
The SIMD types support may be considered a little grey, but I've
encountered loads of general D users who appreciate the SIMD work already,
and while it's certainly not trivial, it's nowhere the mammoth scale of
task auto-vectorisation would be. I can't see it as a loss for the language
or the community, and again, it has further enabled our consideration of D
commercially; which I'd like to think is a general goal for the language.
I know plenty of you don't care about me or my industry, but I maintain
that it's an entire industry in desperate need of salvation from C++,
there's a lot of potential in the games industry to get fantastic value
from using D, and I'm interested in proving that it's a realistic
consideration.
I'd also like to note that we are also very conscious of the time Walter
and other contributors have kindly offered to our support, and we are
hopeful to be able to give reasonable value back to the community should it
all go well for us, in whatever way that manifests...
On 2 November 2012 11:01, Jens Mueller <jens.k.mueller gmx.de> wrote:

Jacob Carlborg wrote:

On 2012-11-01 23:51, Walter Bright wrote:

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

This is quite interesting. Manu comes in from basically nowhere and
fairly quickly manage to convince Walter to implement at least two
feature requests, this one and the SIMD support. I'm not saying that
they shouldn't have been implemented. Although I think something
like AST macros could possible solve issue 8108 and a whole bunch of
other features, a few already present in the language.

I had the same thought when reading this. Very disappointing. An issue
with zero votes is fixed instead of more important ones. Why do I vote
anyway?
Regarding SIMD I have the feeling that because it is built into the
compiler static vectors have actually failed what they promised. I
thought D proposed a portable way of vector operations such that you
write
float[4] = a[] + b[]
and the compiler generates SIMD code for you.

As I mentioned above, I think that is a MUCH larger task, and probably
fairly unrealistic in the near-term regardless.
But secondly, it's just not that simple. (I can see Walter has already
addressed it in a previous post)
It's worth considering that a very significant portion of the silicon on
modern processors (well in excess of 50% on some chips) is dedicated to
hardware acceleration of SIMD/media functions. Until recently, D simply
offered no mechanism at all to interact with half of the silicone in your
box. That's a massive language hole.
At least as a starting point, low level access to this hardware is vital.
Portable libraries can be built using this technology, which are
immediately useful.
The definition of hardware SIMD types doesn't rule out possible future
auto-vectorisation either. And you can probably access auto-vectorising
backends right now if you use GDC or LDC.

Some complexity comes from the
desire to do more and more. As example see this recent request from Manu,

What about all your feature requests? I think you've made more than
anyone, by a factor of 10 at least!
:-)
As for Manu's request
http://d.puremagic.com/issues/show_bug.cgi?id=8108
I've gone over with him why he needs it, and there's no other reasonable
way. He needs it for real code in a real application.

I'd argue this actually is part of a category of features that does not
increase the complexity of the language (quite the contrary in fact).
This is because stating that declaration+definition in the same file
won't work takes actually more cognitive load than just allowing it.
By the consistency principle, one should infer unknown parts of a
complex system from knowing the others. Consider then this setup:
* Declarations (without definition) of functions are allowed.
* Definitions are allowed.
* Declarations and definitions are allowed in distinct files in the same
project as long as they match.
At this point, it is more tenuous to argue that "same file" is a special
case that should prevent declarations and definitions to coexist, than
to just let it happen and let the consistency principle take care of
explaining it.
Andrei

It's unfortunate that there's still bad press circulating about
a situation that is long gone. I suppose you just have to try
and ignore those people.
A more interesting comment is this one:
"But the real problem here is that in order to achieve even
that, the complexity and amount of concepts you have to deal
with in C++11 is mind boggling."
The same is true in D. Well-written D code often does look
rather elegant, but the amount of understanding needed to write
beautiful D code is staggering.

I think that is the case of any multi-paradigm language. It is
already enough to allow both functional and OO style of
programming to have hundreds of things to think about... That is
exactly one of the major reasons why people prefer Java over
other languages...